weight placement ?

[davet]

If you took a car body and weighted it with 12 cubes behind axle, wheel weights (weights attached to the side of the body within the wheel cavity) and as much weight just ahead of the front axle as possible then say a single cube further up to get a 3/4" COM, would that same body perform the same with 10 cubes behind axle, 12 just ahead of axle and no wheel weights? I'm just wondering if the same car body performs the same no matter how you place the weight as long as the COM is the same on each setup. Assuming all the weight is centered side to side in the car and not offset.

If so then I think that wheel weights or plates under the rear axle are only an advantage if the goal is to run a lower COM that isn't attainable by placing 12 cubes behind the axle.

OR, is there something else at work besides COM that makes added weight at the axle line advantageous?

[ngyoung]

There are a few benefits supposedly that the wheel weights have. Bring the weight out to the sides can give more stability like a tight rope walker using a long pole for balance. They also provide an aerodynamic effect acting as a wheel cover. They are still pretty new so a definitive winning configuration hasn't really been flushed out using them. Since the weight is centered around the axis you could also get away with going more aggressive with your COM. I believe Laserman himself or one of the guys that helped test them out was able to get away with just adding any additional weight to the back and not even make a weight pocket in front of the axle.

[davet]

I wonder about the aerodynamic effect as they don't fit inside the wheel but, instead, fill the gap between the wheel and body. Doesn't this push more air? Maybe one could create a fender that directed air not just around the outside of the wheel but also inside, around the weight.

[sporty]

Its going to also slightly lower center of mass. Not much. But a little.
The weights do not stick out of the wheel. The puma car I just made. See pics. I didn't add a spacer, but next time I will.

To answer your question. You can have a balance point is the same, but it does make a slight difference on how you place it.
The bigger factor is the nose weight. Front end weight.

For some reason. I have noticed cars with the same balance point, but when I finger lift the front end. I can tell which car has lighter front end.
Hope this helps some.

It may also help reduce sonic and micro vibration.

[Speedster]

davet, to answer your 1st question, I would say no. The car body will not perform the same. A very brief background. At the beginning of the summer I built a car so I could move weight from front to back and side to side. I used double face tape to hold the weight and Maximum Velocity's 4091 set of wheels which includes his 4094 axles. Stock wheelbase, slots, 3 wheel rail rider. My goal was to use only the 2 tungsten blocks available at the time because I thought it would make it very easy for a scout. It did not work out. Each time I changed positions of weight, the speed would change. Tungsten plates, cubes, and blocks were used along with tungsten putty. Each set-up was run 6 times. Here are the specs on its fastest speed.
COM - 3/4"
1.54 oz tungsten behind rear axle slot
2.33 oz in front of rear axle slot
DFW weight - .68 oz
RR wheel weight - 1.80 oz
LR wheel weight - 2.52 oz
I know this car is fast because I've kept many records in the past 4 years at our District races. Maximum Velocity has come out with the Tungsten block that I've wanted for sometime. I have a second car under construction where I'll be using one or more of Max-V's blocks. Sometimes we do things and think it's great but the Laws of Physics do not always agree with our thinking. If I'm not mistaken, Derbytalk told me long ago that 1 1/2 ounces of weight behind the rear axle slot was the preferred amount for a stock wheelbase car. Funny how that worked out.
Anyhow, that's what all my walking showed me. Best of Luck to you and your scout .

[sporty]

I think I said 1 1/2 in the rear for stock wheel base cars. Worked well for me.

[aphonos]

Here are the specs on its fastest speed.
COM - 3/4"
1.54 oz tungsten behind rear axle slot
2.33 oz in front of rear axle slot
DFW weight - .68 oz
RR wheel weight - 1.80 oz
LR wheel weight - 2.52 oz
I know this car is fast because I've kept many records in the past 4 years at our District races. Maximum Velocity has come out with the Tungsten block that I've wanted for sometime. I have a second car under construction where I'll be using one or more of Max-V's blocks. Sometimes we do things and think it's great but the Laws of Physics do not always agree with our thinking. If I'm not mistaken, Derbytalk told me long ago that 1 1/2 ounces of weight behind the rear axle slot was the preferred amount for a stock wheelbase car. Funny how that worked out.
Anyhow, that's what all my walking showed me. Best of Luck to you and your scout .

Speedster,

Thanks for sharing precise measurements.

Is the DFW left or right? I'm assuming left.

Does "stock wheelbase" mean stock distance and stock location or does it mean only stock distance (i.e. you push the rear axle back to 5/8" as well, but maintain 4 3/8" between the axles)?

How much faster was this setup than your 2nd fastest?

(Yes, I know not to just simply replicate your weighting, because it will vary with another chassis or build.) Thanks!

[Speedster]

The DFW is on the right side. The left front wheel is off the ground and not supporting any weight.
The wheelbase is stock distance and stock location. The one test made with "shifted wheelbase" I did not cut off the back and move it to the front. I simply extended the front 1/4" with a small piece of craft stick (popsicle stick) to see what would happen. It didn't make any difference which surprised me. I thought it would make a significant change in speed. Perhaps the set-up was too crude to give it a fair chance.
All tests were run down Lane 1 of my wood track with Microwizard timer.
Fastest times
2.818
2.814
2.816
2.822
2.816
2.823
2nd fastest
2.827
2.839
2.828
2.838
2.829
2.835
When the test was run with the 1.8 oz block behind the rear axle and the 2.0 oz block in front of the rear axle with .198 oz of tungsten putty on top of the 2.0 block the times were all in the 2.84
and 2.85. It was a lot of fun and educational for me. We'll see how my 2 scouts do in the 2015 races.

[davet]

davet, to answer your 1st question, I would say no. The car body will not perform the same. A very brief background. At the beginning of the summer I built a car so I could move weight from front to back and side to side. I used double face tape to hold the weight and Maximum Velocity's 4091 set of wheels which includes his 4094 axles. Stock wheelbase, slots, 3 wheel rail rider. My goal was to use only the 2 tungsten blocks available at the time because I thought it would make it very easy for a scout. It did not work out. Each time I changed positions of weight, the speed would change. Tungsten plates, cubes, and blocks were used along with tungsten putty. Each set-up was run 6 times. Here are the specs on its fastest speed.
COM - 3/4"
1.54 oz tungsten behind rear axle slot
2.33 oz in front of rear axle slot
DFW weight - .68 oz
RR wheel weight - 1.80 oz
LR wheel weight - 2.52 oz
I know this car is fast because I've kept many records in the past 4 years at our District races. Maximum Velocity has come out with the Tungsten block that I've wanted for sometime. I have a second car under construction where I'll be using one or more of Max-V's blocks. Sometimes we do things and think it's great but the Laws of Physics do not always agree with our thinking. If I'm not mistaken, Derbytalk told me long ago that 1 1/2 ounces of weight behind the rear axle slot was the preferred amount for a stock wheelbase car. Funny how that worked out.
Anyhow, that's what all my walking showed me. Best of Luck to you and your scout .

Very interesting numbers Speedster. These are our numbers from last year. I got them by using 2 identical, calibrated scales. I used the COM Visualizer to get the accurate COM number. We came in 7th place out of over 3,100 cars.

Wheelbase: 5 5/8"
COM: .725
Tungsten behind rear axle: 12 cubes totaling 2.04 oz
Tungsten ahead of rear axle: 9 cubes totaling 1.53 oz ( around .10 oz tungsten putty added ahead of rear axle for tuning)
Left side DFW, weight: .65 oz
Right rear wheel weight: 2.55 oz
Left rear wheel weight: 1.84 oz
Total weight of car: 5.04 oz at weigh in
Drift set at: 4" over 4 feet.
Stock BSA axles with bent rears at 1.5 degrees.
Stock BSA wheels
Oil